1. Field of the Invention
This invention relates to the field of masonry building construction and, more particularly, to lintels used to span the top of openings in a masonry wall to supply superincumbent support for the weight of upper structures.
2. The Prior Art
In masonry construction, precast lintels are often used to span the opening over doors and windows and to provide superincumbent support for the subsequently emplaced building structure over the opening. However, particularly for spanning relatively lengthy openings as may be encountered, merely by way of example, in the construction of a garage door opening, the load-bearing requirements preclude the use of precast lintels. Stronger lintels of higher load-bearing capacity may be constructed "in place" by providing a temporary or permanent support frame as the lintel is fabricated from masonry blocks. Typically, in such a case, special masonry blocks, each having an elongated cavity opening inwardly along the full length of its lower surface and having an inverted "U" cross section, are then used as the lintel after being filled with concrete reinforced with steel bars. The need to provide a framework for the special lintel blocks is time consuming, whereas, on site construction may leave much to be desired in achieving the required load bearing capacity of the fabricated lintel.
In recognition of these problems, in order to eliminate the need for framework structures and to assure construction of lintels having known load-bearing capacity, contractors often resort to built up lintels utilizing an internal reinforcing steel structure which bridges the opening and provides the necessary support for the masonry blocks utilized to complete the lintel. Several forms of this type construction are known. A first, made of 12-14 gauge steel, comprises an inverted "U"-shape section joined (as by welding) to a relatively wider base support flange member which acts as a broad bearing surface and rests on the masonry on opposite sides of the opening to be spanned. Gusset plates may be provided for added structural rigidity to increase the load bearing capacity. However, the welding of the gusset plates into position requires a significant amount of hand labor and set up time. The process is, as a result, very time consuming and expensive. A second known lintel preform has the general shape of an "I"-beam and includes two horizontal flanges joined by a vertical web. In this case, the web is usually constructed of 12-14 gauge steel; however, the thickness of the horizontal flanges may vary from less than 1/8 inch to more than 1/2 inch, depending on the length of the span to be bridged and the requisite load-bearing capacity. Thus, the manufacturer of such lintel preforms requires multiple set ups and manual operation which is, again, both time consuming and expensive.
With either construction, the base flange rests at both ends on masonry adjacent the span to be bridged. The preform is then encased in special masonry units which define the exterior dimensions of a built-up lintel. The space between the inner surfaces of the masonry units and the outer surface of the lintel preform is then filled with mortar.
Despite the increased convenience and assurance provided by the use of the self-bridging, reinforced steel forms, such steel bridging forms represent, in and of themselves, a significant expenditure of time and effort in their fabrication. It is also well recognized in the prior art that various modifications must be made to the reinforcing steel bridging structure as the width of the opening to be bridged and the bearing load to be supported increases. Frequently, in cases of long spans or high bearing loads, the contractor is forced to practice a form of "over-kill" by selecting the bridging/reinforcing structures available to him. He will often have to resort to a much heavier and stronger structure than is necessary, because there is no structure of intermediate design available to meet his construction criteria.
Thus, it will be apparent to those skilled in the masonry construction art that it would be highly desirable to provide a lintel system characterized by relative simplicity of construction, very high load-bearing strength and adaptability to providing superincumbent support for spans of different lengths and to accommodate different load bearing requirements. It is to these ends that this invention is directed.